1. Field of the Invention
The present invention relates generally to an electric adapter, and in particular to an electric adapter having DC (Direct Current) outputs of different voltage levels.
2. Description of the Prior Art
Mobile electric appliances, such as mobile phones and notebook computers, are provided with a built-in power source comprised of rechargeable batteries. The mobile electric appliance can also receive power from an electric main or other external power sources. For example, some of the passenger airplanes provide power sockets in the passenger seats. Another external power source that is readily available is the electric power socket provided on an instrument panel of a car. To receive power from such external power sources, an adapter system is required for each particular mobile device that is mechanically and electrically compatible with the adapter system. Of particular concern of the adapters is the output level of voltage which must be corresponding to the rating voltage of the mobile device in order to properly drive the mobile device and not to cause damage to the mobile device due to excessive voltage level.
An adapter system for selectively providing DC outputs of different voltages is available in the market. The conventional adapter system comprises a number of individual connectors selectively and exchangeably coupled to the adapter system. Each individual connector comprises a resistor of different resistance. Different resistances of the connectors, once coupled to the adapter system, provide different feedback signals which in turn change the output voltage level of the adapter system. It is, however, difficult for a manufacturer to incorporate a resistor in the separate connector. Further, the manufacturer must make a number of different connectors that have different resistors mounted therein. This increases costs of manufacturing and storage.
Further, a user must purchase a number of different connectors that have different resistors therein for obtaining DC outputs of different voltage levels.
It is thus desired to provide an electric adapter system for overcoming the above problems.
An object of the present invention is to provide an electric adapter system comprising a voltage level control circuit and a feedback circuit, both arranged inside an adapter casing, a connector releasably engageable with the adapter system changing the overall resistance of the feedback circuit that in turn change the output voltage levels of the voltage level control circuit, whereby the voltage level of the output of the adapter system is changed.
Another object of the present invention is to provide an electric adapter system comprising a switching device allowing a user to manually and selectively changing the overall resistance of the feedback circuit in order to change the voltage level of the adapter system.
To achieve the above objects, in accordance with the present invention, there is provided an electric adapter system comprising an adapter including a circuit connected between input and output connection devices respectively connectable with an external power source and a power consuming device. The output connection device is mateable with a connector forming an output member for engaging the power consuming device. The circuit comprises a voltage level control device and a feedback device. The voltage level control device supplies an output voltage to the output connection device via positive and negative power terminals. The feedback device comprises a plurality of voltage selection lines each having a different electric resistance whereby by selectively connecting one of the voltage selection lines to the negative power terminal, a feedback signal is generated by the feedback device and applied to the voltage level control device for changing the voltage level of the output voltage of the voltage level control device.